Nonlinear optical crystal is one of the important photoelectric information functional materials, the important material basis of photoelectric technique especially laser technique. Nonlinear optical crystal is useful in conversion of laser frequency, broadening the wavelengths of lasers; regulating the intensity and phase of laser; attaining the holographic storage of laser signal, avoiding the self-pumped phase conjugation of distorted wavefront, etc. Accordingly, nonlinear optical crystal is an essential material in the advanced technique and modern military technique, whereby is put in the preferential development position in developed countries, and scheduled in the high technique development plans as an important strategic measure with high attention and supporting.
With the development of laser technology from 1960's up to date, the nonlinear optical crystal has been rapidly developed. Meanwhile, several nonlinear optical crystals such as, lithium niobate, potassium dihydrogen phosphate, potassium dideuterium phosphate, lithium iodinate, potassium titanium phosphate, barium metaborate, lithium triborate, potassium niobate, cesium borate, lithium cesium borate, beryllium potassium fluoroborate, etc. have been developed increasingly since the first quartz frequency multiplication crystal, and been widely used in the fields of second harmonic generation, sum-frequency, difference-frequency, optical parametric amplification as well as electro-optical modulation and electro-optical deflection, etc.
Development of all-solid-state deep ultraviolet (200 nm) coherent light sources is one of the most advanced research projects in the current international photoelectron field, because of the exceedingly important applications of ultraviolet laser in varieties of high technique fields, such as, the requirements of all-solid-state ultraviolet coherent light sources in the new generation of integrate circuit; the active demand in the photoelectron energy spectroscopy and spectroscopy techniques for tunable all-solid-state ultraviolet light sources, which will play an essential role in promoting the development of deep ultraviolet spectrum and energy spectrometer and will create a new researching field of material science; and also the great potential of driving the progress of the laser fine machining. Since no laser crystal which outputs deep ultraviolet wavelength has been developed, the key point of solving the solid-state deep ultraviolet source is focused on the development and application of NLO frequency conversion crystals in ultraviolet wavelength range. In these circumstances, the present inventors have conducted intensive studies and finally found a new non-linear crystal K3B6O10Cl capable of attaining a 4-harmonic generation of 1064 nm.